Inquiring Minds

Questions About Physics

Isolating quarks

Ben, You asked:
my name is ben thompson and i am student teaching at downers grove north
high school. we are doing a unit in electromagnetism and somehow came
upon the concept of the quark. i did some web research only to find out a tiny
bit about quarks and leptons.

the question that one of my students stumped me with was whether or not
the scientists at fermi lab have isolated any quarks yet. i do not know,
and we have decided to allow you (the knowledgeable) to help us out. if
you have the time, will you please help us in our research?

thank you for your time.

sincerely, and in dedication to science,

-ben

Dear Ben,

Thank you for your question. Quarks are very peculiar
particles. They are more basic (fundamental, elementary) than protons and
neutrons. Protons and neutrons and many other particles are built of
quarks,
held together by a VERY strong force
MUCH stronger than gravity or electromagnetism) which we actually call
"the
strong force". In a sense we can "see" the quarks inside a proton by
shooting electrons at the proton. Some of them scatter off sideways or
even
backwards, which is only possible to explain if there are little (like
points, or almost) objects inside the proton and much smaller. If the
proton
was just a "soft blob" the electrons would never scatter backwards like
that. So you might think that you could knock a quark out of a proton by
firing electrons at it. But all the experiments we have done at Fermilab
and
elsewhere in the world (there is another big laboratory in Geneva,
Switzerland called CERN, for example) looking for isolated quarks have
never
seen one. If you see the scatterd electron you can work out the direction
the quark would have gone, but instead of a quark you see a narrow spray
of
the composite particles that contain
morequarks themselves. Nearly all physicists believe that quarks can never
be isolated.
It's as if when you try to kick a quark out of a proton, the strong field
that was holding it in gets stretched, rather like an elastic band.
Eventually the elastic band breaks, and at the break a new quark (actually
a
quark-antiquark pair) is created out of the energy in the field. The idea
that quarks can never be isolated is called confinement.

By the way we know of six types of quark, and we have good reasons
to believe that that is it, there are no more types to discover. We call
them up, down, strange, charmed, bottom and top. The last two were
discovered at Fermilab. Each type of quark has an antiquark, and
quark-antiquark pairs can be created out of energy in particle collisions.